Convicted Cleveland kidnapper Ariel Castro was found hanging in his jail cell with his pants and underwear around his ankles, leading investigators to question whether he killed himself while attempting autoerotic asphyxiation, according to an internal investigation into his death.

Castro said he was addicted to sex during his sentencing for holding three women captive in his basement for a decade.

Two correction officers have been put on administrative leave and a criminal investigation is pending.

"I'm not a monster. I have an addiction, just like an alcoholic has an addiction," Castro said at his sentencing hearing.

The plea deal spared him the death penalty and he was sentenced to life in prison.

An internal investigation into how Castro was able to kill himself Sept. 3 under the watch of jail guards reported that corrections officers on duty the night of Castro's death skipped their rounds and falsified reports about how often they checked on him in the hours before his death.

The officers reported that Castro was safe in his cell at 8:45 p.m., according to the report. They checked on him again at 9:15 p.m., at which point they found him hanging from a window hinge by a bedsheet wrapped around his neck, according to the report.

Castro also had photos of his family members neatly arranged on the floor of his jail cell, as well as a Bible open to the Gospel of John, Chapters 2 and 3, which reference Jesus turning water into wine, overturning tables of moneymakers at the temple, and the story of Nicodemus.

Corrections officers pulled Castro down and cut the sheet off his neck, performed CPR on Castro and called an ambulance. Medics could not revive Castro, the report said.

The report said there was no obvious motivation for the suicide. He had complained about verbal harassment from other inmates and staff at the jail, and feared that someone was tampering with his food, but investigators said his fears were unfounded.

The doctor who performed the autopsy on Castro said she is certain that he committed suicide, even after reading the new report.

"I am 100 percent certain that he killed himself and even if I reconsidered the manner of death at this point it would be undetermined," Dr. Jan Gorniak, the Franklin County Coroner, told ABC News.

Earlier in the day, before killing himself, Castro had a hearing with the jail's warden over protective control. At the hearing, he "appeared happy" that being put in protective control would place him closer to his family for visits, and asked about receiving mail. He was returned to his cell shortly before 2 p.m., just seven hours before his death.

Castro was arrested in May after the three women escaped from his basement. They had all been kidnapped by Castro between 2002 and 2004 and either chained in his basement or confined to cell-like rooms upstairs. He frequently raped them, according to prosecutors.

In May, a neighbor heard Berry screaming from behind a locked door and helped free the women.